In recent years, powder coatings have become increasingly popular because these coatings are inherently low in volatile organic content (VOC), which significantly reduces air emissions during the application process. Epoxy condensation polymers, vinyl chloride polymers and acrylic resins have been used as the main film-forming polymers for these coatings. The advantage of the acrylic resin system over the epoxy condensation polymers and vinyl chloride polymers is that acrylic resins provide superior outdoor durability, are more resistant to heat and have better solvent and chemical resistance. The use of glycidyl functional acrylic resins provide such desired properties.
There is a need to apply powder coatings compositions in the automotive original equipment manufacturing (OEM) process. In today's competitive market, automobile manufacturers are placing stricter requirements on coatings properties and performance. Good exterior durability, acid etch and water spot resistance, and excellent gloss and appearance are typical examples. Currently, these properties can be achieved using epoxy-acid cured liquid coatings. However, liquid coatings have significantly higher VOC levels than powder coatings which essentially have zero VOC levels.
Although epoxy-acid systems are known for powder coatings, they are presently not widely used commercially for automotive OEM clear coatings because of inferior appearance, poor flow, and poor cured film properties. In addition, these coatings often have poor stability prior to the application process.